WEST KIMBERLEY PLACE REPORT - Department of Sustainability ...

From research focused on fragmented rainforest patches in the NT, Price (2006)
argues that in the long term, many rainforest plant populations depend on the dispersal
of seeds by frugivorous bird species. The species examined in this research are mostly
shared with the Kimberley. The widespread nature of this rainforest/frugivore
interdependence across northern WA and the NT makes it difficult to demonstrate that
the vine thickets of the Kimberley are any more important for birds and bats than
other areas of northern Australia. The refugial role of the closely associated mesic
Kimberley mangroves communities in maintaining populations of birds and bats is
discussed in mangroves refugia below.
The low degree of endemism associated with Kimberley rainforest plants and
vertebrates is in contrast with a much higher level associated with invertebrates. Many
of the small immobile invertebrate species endemic to the Kimberley have only been
recorded in its rainforest patches; this includes 90 per cent of the earthworms and 48
per cent of the land snails (Kenneally and McKenzie 1991). It is speculated that the
cooling and drying of the Kimberley, since the early Miocene (c. 20 million years
ago), led to a shrinking of the then more extensive rainforest into the isolated patches
present today (Köhler and Gibson 2009). When the rainforests shrank into these
patches they became evolutionary refuges (Morton et al. 1995) for associated
invertebrates (Köhler and Gibson 2009).
Survey and taxonomic work by Solem (1979, 1981, 1984 and 1985) and more recent
research (Graham 2001b; Köhler 2010) have helped highlight the national importance
of the Kimberley Plateau and adjacent islands for land snail richness and endemism.
These species are largely found in vine thickets. ANHAT analyses have supported the
findings of these researchers, showing the Kimberley Plateau is exceptionally high in
richness (with 120 species discovered to date in the Kimberley) and endemism for
Camaenidae (air breathing land snails). Restricted or locally endemic Camaenid snails
are found frequently in Kimberley vine thicket surveys, including the more
geographically isolated Dampier Peninsula dune thickets, as far south as Broome.
Researchers (Köhler 2009; Köhler and Gibson 2009.) speculate that this consistent
spread of now locally restricted species reflects long-term evolution through isolation,
with the once more widepread Kimberley rainforests of the warmer, wetter Miocene
contracting and fragmenting as the region became cooler and drier. Snail populations
became isolated as their communities reduced to small islands of rainforest
surrounded by drier, less habitable savanna woodlands. The remnant thickets became
refuges for the development of their very own sets of species. It is further speculated
that once isolated, this promoted parallel patterns of invertebrate radiation (i.e.
explosive evolution of species groups) and adaptation (Köhler and Gibson 2009).
Not only is the Camaenid species endemism high within these Kimberley rainforest
refugial pockets but the phylogenetic diversity has shown evidence of generic (genus
level) endemism (Solem and McKenzie 1991), with Torrestitrachia, Amphlirhagada,
Setobaudinia, Baudinella and Rhagada found exclusively, or nearly so, within the
region (Solem 1979, 1981, 1985). Recent work by Köhler (2010) described two new
genera Kimberleydiscus, Kimberleymelon, both endemic to the Bonaparte
Archipelago, further adding to this diversity. This higher level endemism and the
diversity of Camaenid snail species is reflected in ANHAT analyses, which centre on
the Prince Regent Nature Reserve, and the coast from Augustus to Bigge Island, and
the Devonian reefs in the west Kimberley. Camaenid snails found outside this core are
90